time的一个问题

请问各位，time.clock()的作用？

Type:                builtin_function_or_method
Base Class:        <type 'builtin_function_or_method'>
String Form:        <built-in function clock>
Namespace:        Interactive
Docstring:
    clock() -> floating point number
   
    Return the CPU time or real time since the start of the process or since
    the first call to clock().  This has as much precision as the system
    records.

这个应该不难理解吧……